From Arundo donax L. we have isolated the new dimeric alkaloid arundinine, with the composition C23H28N4O, the structure of which has been established on the basis of its physicochemical characteristics and 1H and 13C NMR spectroscopy, including 1D and 2D experiments in both homo- and heteronuclear regimes. The proposed structure - 3a-(3′-dimethylaminoethylindol-5′-yloxy)-1-methylpyrrolidino[1a,3a - b]indoline - has been confirmed by x-ray structural analysis (XSA).